Method of preparing a smokable material



United States Patent 3,516,416 METHOD OF PREPARING A SMOKABLE MATERIAL Theodore S'. Briskin and Geoffrey R. Ward, Beverly Hills,

Calif., assignors to Sutton Research Corporation, Los 5 US. Cl. 131-2 3 Claims ABSTRACT OF THE DISCLOSURE A method of forming a smoking product formed of cellulosic materials is disclosed in which one of the preliminary steps includes the selective oxidation of the cellulosic material with liquid nitrogen dioxide under conditions to effect substantial conversion of the C methylol groups. The nitrogen dioxide used in the oxidation is present in a ratio of 5 to 1000 parts by weight to one part of the cellulosic material and the reaction is carried out at a temperature of between and 65 C. Preferably, the moist nitrogen dioxide is first rinsed out of the cellulose material with dry nitrogen dioxide.

This is a continuation-in-part of our copending applications Ser. No. 595,622, filed Nov. 21, 1966, and entitled Smoking Products, now Pat. No. 3,447,539 and Ser. No. 674,994, filed Oct. 12, 1967, and entitled Smoking Products and Process for Making Such Products.

As used herein, the term smoking products refers to and includes filler materials used in the production of cigarettes, cigars and for filling pipes and mixtures thereof with various proportions of tobacco and cigarette papers and wrappers used in the preparation of and which are burned during the smoking of sugh cigarettes, cigars and the like, and it includes the cigarettes, cigars and the like products manufactured thereof.

In the aforementioned copending applications, description is made of the preparation of a smoking product suitable for cigarettes, cigars or pipes, in which relatively pure cellulosic material is subjected to selective oxidation with liquid nitrogen dioxide to convert more than 90% of the free methylol groups on the cellulosic molecule to carboxyl groups to yield a product which can be referred to as an oxycellulose. The oxidation reaction product is further processed by removal of liquid nitrogen dioxide by vaporization and copious washing of the oxidized product with water and/ or alcohol for removal of solubilized foreign materials and decomposition of nitrites and nitrates, and/or treatment with solvents such as acetone for removal of oils, waxes, latices and the like which impart undesirable taste and odor when the product is used as a smoking product in accordance with the practice of this invention.

As further described in the aforementioned copending applications, the oxidized and cleansed cellulosic derivative is further processed by a reduction reaction with a hydride or borohydride of an alkali or alkaline earth metal, such as sodium or lithium borohydride, for reducing groupings which otherwise have a tendency to evoke unpleasant odors or taste as the product is burned. The product before or after being processed by the described reduction reaction can be subjected to oxidation with peroxide solutions as a means for eliminating further components which contribute undesirable aroma or taste to the burning product.

The resulting oxidized and reduced cellulosic material is then formulated with mineralizing agents in the form of oxalates, glycolates, diglycolates, lactates, pivalates or tannates of such metals as calcium, magnesium, lithium, potassium, barium or strontium, preferably introduced internally in the cellulosic derivative for purposes of providing desirable ashing characteristics, although beneficial ashing characteristics of limited utility can be achieved by external application of such mineralizing agents.

As described, the desired internal application of the mineralizing agents can be achieved by first wetting the fibers with a solution of the desired metallic ion for absorption into the cellulosic derivative, followed by exposure to a solution of the desired anion whereby the corresponding metal salt forms in situ within the cellulosic material.

Maintenance of glow and burning rate, characteristic of natural tobacco, is achieved by formulation to include a potassium salt, such as potassium oxalate, or by the addition of rubidium or cesium compounds in amounts within the range of 1% to 10% by weight but preferably less than 1% by weight, as described in the copending application Ser. No. 623,528, filed Mar. 16, 1967, and entitled Smoking Products and Process for Their Manufacture. Smoke generators can be added to increase the visual effect of the smoking product when burned.

The resulting product is suitable for use as a smoking product alone or in admixture with tobacco to produce a smoking product having better taste and less undesirable ingredients.

This application will be addressed to a process for treatment of the cellulosic material with liquid nitrogen dioxide to effect selective oxidation of methylol groups to carboxyl groups in forming an oxidized cellulosic derivative suitable for use in the preparation of a smoking product.

The features of this invention reside in the conversion of a cellulosic material to a product which is desirable for use in smoking and which finds wide acceptance as a smoking product from the standpoint of taste, aroma, appearance, burning characteristics and relative absence of harmul ingredients or combustion products.

As the cellulosic raw material, use can be made of the various forms of cellulose, such as wood pulp, flax, straw, fibrous carbohydrates, seaweed carbohydrates, bamboo filaments, cotton filaments, filamentous gums, rayon, a1- phacellulose, refined paper, hemp, and even plants and plant leaves and the like fibrouse materials in which the cellulose components have been separated and purified. It is preferred to make use of a purified cellulose from which the various sugars, proteins, chlorophylls, colors, lignins, oils, waxes, resins and latices have been removed since these materials lend considerably to undesirable odors and taste from the smoking product.

Purified cellulose is unsatifactory by itself for use in smoking, at least from the standpoint of taste, smell and burning characteristics. These undesirable properties are believed to stem from acids and aldehydes that are evolved upon pyrolysis of the cellulosic material. It has been found that these defects in pure cellulose can be greatly alleviated by conversion of the free methylol groups to carboxyl groups to produce a product which readily pyrolyzes by complete breakup of the molecule into water vapor and oxidation products of carbon such as carbon dioxide and low molecular weight compounds which readily volatilize. Thus the object of this invention is to achieve a selective oxidation of the cellulosic material or carbohydrate to convert free methylol groups, especially the methylol group on the C carbon, to varboxyl groups, preferably with better than conversion. There is no objection to oxidation numbers of greater than attributed to conversion of secondary hydroxyl groups as on the C and C positions to monoand diketo groups, but We prefer to avoid cleavage of the molecule.

Selective oxidation of carbohydrates without degradation is difiicult to achieve with oxidizing agents, such as peroxides, periodic acid, hypochlorites, permanganates, dichromates and the like. On the other hand, selective oxidation for use in the preparation of smoking products from such cellulosic materials or carbohydrates, hereinafter referred to as cellulosic materials, can be achieved with nitrogen dioxide. Gaseous nitrogen dioxide has been found to be impractical for this purpose for the reason that the oxidation reaction is extremely slow and it is commercially impractical to stock the cellulosic material so as to permit complete access of the gaseous nitrogen dioxide, with the result that it is difficult to provide the desired rate of conversion and conversion is not uniform throughout the cellulosic material, thereby resulting in an undesirable product. Further, the oxidation reaction is an exothermic reaction that is accompanied by the generation of heat which is not easily dissipated with gaseous nitrogen dioxide. As a result, hot spots can develop which lead to degradation and even confiagration of the cellulosic material. Further, the acid liquor produced is relatively high boiling and as reaction proceeds, the carbohydrate is subjected to increasing concentration of adsorbent acid liquor which is degradative rather than adsorbed nitrogen dioxide which would not be degradative.

On the other hand, it has been found that liquid nitrogen dioxide gives an oxidation reaction that has the desired selectivity and that complete wet-out of the cellulosic material is achieved almost instantly whereby the oxidation reaction can take place substantially uniformly throughout the cross-section of the cellulosic material and at a much more rapid rate whereby a more uniformly and more completely oxidized product is obtained. Further, liquid nitrogen dioxide, when used in proportions suitable for the practice of this invention, operates as a quench immediately to dissipate heat generated by any localized exothermic reactions.

It has been found that the course of the oxidation reaction and treatment of the oxidized product can be influenced by a number of very important factors which are incapable of being adapted to reaction with gaseous nitrogen dioxide but which can be employed to advantage in oxidizing with liquid nitrogen dioxide thereby greatly to enhance the oxidation process, including increase in reaction rate, increase in the amount of conversion, uniformity of oxidation, as well as purification and subsequent treatment of the reaction product, as will hereinafter be described.

In accordance with the practice of this invention, the oxidation of preferably purified cellulosic materials is carried out by suspension of the cellulosic material in liquid nitrogen dioxide in the ratio of 1 part by weight cellulosic material to to 1000 parts by weight of liquid nitrogen dioxide and preferably 1 part by weight of cellulosic material to 25 to 50 parts by weight of liquid nitrogen dioxide, often referred to as N 0 The reaction is carried out at a temperature within the range of to 65 C. At a temperature below 15 C., the rate of reaction is too slow for commercial practice and excessive amounts of hydrolytic cleavage is experienced. At reaction temperatures in excess of 65 C., the oxidation reaction becomes less specific and undesirable side reactions take place to produce excessive amounts of un desirable byproducts. Since the reaction rate increases almost three-fold per each 10 C. increase in temperature, it is desirable to make use of a reaction temperature which is as high as practical but other factors limit the use of high temperatures. In the preferred practice of the invention, use is made of a temperature above C. and preferably within the range of to 45 C. At reaction temperatures above 21 C., it is necessary to make use of a closed pressure system since the liquid nitrogen dioxide boils at 213 C. at atmospheric pressure. Thus while it is desirable to carry out the reaction under pressure, it is essential to operate under pressure when the reaction temperature exceeds 21 C. The pressure can vary from the vapor pressure of the liquid nitrogen dioxide at reaction temperature up to high pressures consistent with the ability of the apparatus to withstand such pressures. It is preferable, in batch processing, to permit a vapor space to exist, although this is generally not so in continuous processing of slurried material.

The effects of temperature on pressure and reaction rate of shredded paper are found to be as follows. For example, at 21 C., one atmosphere of pressure is generated and four to eight days are required for conversion in a system containing 1 part by weight of cellulosic material per 50 parts by weight of liquid nitrogen dioxide. At 40 C., the pressure becomes 30 to 50 p.s.i., and better than 90% conversion can be achieved with the same materials in one day. At a temperature of 50 C., the pressure becomes 60 to 75 p.s.i., and the time is reduced to four to five hours. A shorter reaction time suitable for continuous processes can be achieved by operating at temperatures within the range of 45 to 65 C. and at autogenous pressure or higher.

It has been found further that a small amount of water is released during the oxidation reaction and that the moist nitrogen dioxide liquid becomes acidic and highly electrically conductive when cooled so that it is capable of bringing about progressive degradation or attack on the cellulosic material. On the other hand, at elevated temperatures the moist nitrogen dioxide liquid is no n-conductive so that the presence of the water is not harmful to the reaction. This is another important reason for operating at elevated temperatures above 15 C. and preferably at higher water contents, at higher temperatures such that the liquid remains substantially nonconductive. These same factors do not prevail to retard or eliminate the undesirable effects of water generated when using gaseous nitrogen dioxide, since the water stays on the cellulose and the gaseous nitrogen dioxide dissolves in the water to form acids which remain in close contact with the cellulose in the absence of sufficient liquid nitrogen dioxide to dilute it to a level where its activity can be regulated by temperature. Although it is possible to have as much as 8% water in the liquid nitrogen dioxide, when operating at temperatures in the range of 40 to 65 C., it is preferred not to exceed an amount of Water greater than 2.5% to 3% of the liquid nitrogen dioxide mixture. After the reaction, it has been found desirable to rinse the cellulosic material with dry nitrogen dioxide to remove the moist nitrogen dioxide from it, otherwise the moisture level on the cellulose climbs rapidly as the nitrogen dioxide is evaporated off and causes degradation of the cellulose.

Having described the basic concepts of the selective oxidation with liquid nitrogen dioxide to produce an oxidized cellulosic material suitable for use in the preparation of a smoking product, illustration will now be given of the practice of this invention.

EXAMPLE 1 A highly purified commercial grade of wood pulp in the form of thin paper is shredded into strands of about 2 mm. width and immersed in approximately one hundred times its weight of liquid nitrogen dioxide at 20 C. Immersion continues for about five to ten days at this temperature until testing indicates that the carboxyl level of 92% to expressed as polyanhydroglucuronic acid content, is achieved. The testing involves washing in aqueous alcohol, drying, dissolving in excess standard alkali and then titrating back with standard acid solution. The alkali consumption is expressed as a percent content of polyanhydroglucuronic acid in the salt-free, water-free carbohydrate. It should be noted that a virtue of this method is that it measures by hydrolysis those carboxyl groups which may otherwise be temporarily hidden in the form of lactones and internal esters.

The shredded material is then substantially freed of excess nitrogen dioxide by means of a warm stream of dry air. This is followed by soaking the oxidized cellulosic material in aqueous alcohol containing about by Weight oxalic acid for 15 to 30 minutes. Any carbonates, nitrates and nitrites of calcium, present in the oxidized cellulosic material, are thus converted to calcium oxalate, which is interspersed within the oxidized cellulosic material. In this form, the calcium oxalate functions as a mineralizing agent which contributes to the ash of the smoking product.

The content of nitrite and nitrate by-products of the nitrogen dioxide reaction is reduced by hydrolysis during this soaking period and by discarding the solution after it has been drained from the cellulosic derivative. At this point the treated cellulosic derivative can be subjected to an extraction by an organic solvent, such as acetone, to remove undesirable odor producing materials from the oxidized cellulosic product. However, it may be preferable to do this prior to the aqueous treatment.

While the cleansed and oxidized cellulosic material represents material more suitable for use as a smoking product than the purified cellulosic raw material, it is preferable to subject the oxidized and cleansed cellulosic material to further processing as described in the aforementioned copending applications to introduce mineralizing agents, smoke generating agents, glow sustainers, pH control and the like to form the final smoking products which can be used in cigarettes, cigars, or in pipes.

EXAMPLE 2 With reference now to the flow diagram, dry cellulose is loaded into the reactor 1 through a door (not shown) at the top. A partial vacuum is drawn on the reactor by means of a water jet. A weighed amount of liquid nitrogen dioxide is transferred from the liquid nitrogen dioxide storage tank 2 for introduction into the reactor by means of a spray pipe 3 to counteract the heat of absorption of the nitrogen dioxide vapors. During transfer, the pressure equalizing line from the reactor to the storage tank is kept open until transfer is complete. An amount of liquid nitrogen dioxide corresponding to thirty times the weight of cellulosic material is introduced into the reaction system and this amount of liquid nitrogen dioxide is constantly recirculated from the drain 4 at the bottom of the reactor to the spray 3 at the top via the gear pump 5.

The reaction mixture is heated and maintained at reaction temperature of 40 C. by a heat exchange fluid circulated from a reservoir 6 through the jacket 7 about the reactor and a vapor pressure of about 35 to 50 p.s.i.g. is conserved within the reactor.

Reaction is continued for approximately two days to effect conversion of 95% to 98% of the methylol groups. Upon completion of the oxidation reaction, the contents are cooled by circulation of cold fluid through the jacket and the pressure equalizing line is opened so that the liquid nitrogen dioxide can be drained from the reactor for transfer to the auxiliary storage tank 8.

The reaction mass in the reactor is rinsed first with dry liquid nitrogen dioxide from storage with return of the drainage to storage. When rinsing has been completed, the reactor is isolated from the system and residual nitrogen dioxide is removed first by vaporization under vacuum and then by flushing with air circulated through the reactor. The vapors are drawn from the reactor by means of a jet ejector and the nitrogen dioxide is removed from the vapors by scrubbing with alkali.

The converted cellulosic material may then be transferred from the reactor for subsequent purposes, such as solvent extraction, peroxide treatment, reduction with borohydride, mineralizing with calcium oxalate, modification with potassium salts or salts of rubidium or cesium to adjust the burning rate, and modification for pH control, smoke generation and odor, and the like processing steps, as previously described and as more fully described in the aforementioned copending applications.

It will be apparent from the foregoing that we have provided a simple and efiicient means for achieving a selective oxidation reaction for the treatment of cellulosic materials to enable use of such cellulosic materials in the preparation of a smoking product having good taste, aroma and smoking characteristics when used alone or in combination with natural tobacco in smoking products.

It will be understood that changes may be made in the details of formulation and operation without departing from the spirit of the invention, especially as defined in the following claims.

We claim:

1. In the preparation of a smoking product of cellulosic material, the step of reacting the cellulosic material with a medium formulated of liquid nitrogen dioxide to oxidize selectively the C methylol groups of the cellulosic molecule in which the liquid nitrogen dioxide is present in the ratio of 5 to 1000 parts by weight of liquid nitrogen dioxide to one part by Weight of the cellulosic material and in which the reaction is carried out at a temperature within the range of 15 to 65 C.

2. In the preparation of a smokable product of cellulosic material, the steps of reacting cellulosic material with a medium formulated of liquid nitrogen dioxide to oxidize selectively the C methylol groups of the cellulosic molecule and which includes the step of rinsing out the moist nitrogen dioxide using dry nitrogen dioxide prior to removing the remainder of the nitrogen dioxide from the cellulosic material.

3. An oxidized cellulosic derivative adapted for use in the preparation of a smoking product prepared by the process of claim 1.

References Cited UNITED STATES PATENTS MELVIN D. REIN, Primary Examiner US. Cl. X.R. 

